This invention relates to visual detection and warning devices, and more particularly to a visual spoilage indicator for food containers. The invention is especially relevant to inexpensive indicators which may be easily incorporated into common food containers to provide a quick and easily detectable indication of probable deterioration of the food contents within the container.
Hardly a year goes by when there is not an outbreak of botulism in some part of the country. Even though the strictest standards of care may be observed in the preparation, packaging, sealing, and sterilization of foodstuffs and their containers, it is virtually impossible to insure completely against the occasional presence of bacteria. Given enough time (and not much is required), even one or just a few bacteria can create a substantial risk of botulism within the contaminated container. Of course, the public is warned to watch for such signs as swollen cans, but more than this is needed, as proven by the many people who continue to be hospitalized from time to time from botulism poisoning.
Recently it has become increasingly common for manufacturers to date code their products so that, either through sale or removal by the grocer, the products will be limited to a reasonable shelf life. This shelf life is presumably determined by balancing the risk that a contaminated container could become dangerous in a given period of time versus the cost of increasing the reliability of production controls in order to reduce the likelihood of initial contamination. Obviously, it would be unreasonably expensive to be absolutely certain that every container which left the factory was completely and totally sterile. On the other hand, a fair quantity of perfectly good food is probably destroyed when the shelf life expires in order to avoid the risk that one bad container might survive and be consumed. The picture is further complicated since there is no way of determining just how long a particular container might be stored in a given household.
While alternatives to strict production and shelf life controls have undoubtedly been explored, there has been surprisingly little visible progress with repsect to other solutions to this problem. One such alternative solution, as suggested by the present invention, would be the provision of some sort of indicator which would readily and quickly show the condition of the food within the container. Certainly, the matter of displaying the ambient conditions within a particular sub-environment is not, in a broad sense, a new proposition. Fish aquarium thermometers and indoor-outdoor thermometers are common consumer products which provide a few examples. Various devices are also known which indicate the temperature, pressure, and/or humidity conditions within some sub-environment, and detectors are also known for indicating the presence of specific materials under these conditions.
Nevertheless, and put in its simplest terms, one cannot today walk into a supermarket and pick out a can of beans or mushrooms or whatever and tell at a glance whether or not there is a likely risk of botulism poisoning from this food. Obviously, a substantial need in this area has long existed, and continues to exist to this day. Further, from an economic standpoint, a reliable (even if not perfect) and inexpensive detector could well eliminate the need for shelf life controls, thus reducing or eliminating losses from the disposal of perfectly good food products. Additionally, it would substantially reduce the problem and risk resulting from further extending the storage once the product was taken home.
To explore the problem further, when the food within a sealed container starts to spoil, several by-products are given off. It is therefore theoretically possible to detect spoilage by detecting one or more of these by-products. Common to all such deterioration is the production of heat, acidity, pressure, and carbon dioxide (CO.sub.2). Ideally, a spoilage detector should be useable with as many different food products as possible, without requiring different detectors for each different type of food material.
Turning to the first by-product, heat, it is easy to see that a heat detector is not likely to be practical because the heat evolved during spoilage is small. Thus the typical conditions of storage and transportation of many food containers would produce temperature conditions far in excess of those likely to result solely from the heat released during spoilage.
Similarly, acidity is not a preferred index since the pH of various foodstuffs varies widely. It would therefore be necessary to have a full spectrum of indicators in order to accommodate all the different pH levels.
Pressure is perhaps a slightly more workable indicator, but still not very practical. In the first place, due to temperature variations and the chance of mishandling before sale, such a detector would have to be unresponsive to nominal pressure changes. Also, many products are heat sterilized after the can is sealed, so such a pressure detector would have to be insensitive to the pressure increase developed when the can is sterilized. However, the development of substantial pressure occurs rather late in the spoilage process, and therefore, to be effective, it would be necessary for such a detector to respond to slight pressure increases. These are obviously conflicting requirements which make pressure detection impractical.
Thus, if it were possible simply to detect carbon dioxide gas, this would be an ideal way to indicate the likelihood that the food content of the container was deteriorating. Of course, such a detector should be usable with the widest possible variety of foodstuffs. Thus such a detector would have to operate independently of the other properties of foodstuffs, such as pH, salt content (corrosiveness), pressure or vacuum, and so on. Further, such a detector must obviously be approved for use in connection with consumables.